If you train it from childhood, you can train it to be permanant. But if you start as a grown up, yes - you may do the full side split, but usually with a warmup, you can, however, train your front splits to be always ready with no warm up. That's the way it works for me and most of people I know. Also I am a man, for women it's easier. I've been training for about a year. Must train every or every other day, each split for 10-15 minutes.